This application claims the priority of German patent application 196 54 367.3, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for mounting lugs and/or projections on a thin metal sheet, particularly on a thin sheet metal strip, which project essentially perpendicularly from the base of the thin metal sheet and have a height which is higher than the metal sheet thickness, as well as to a thin metal sheet produced accordingly and to a rectangular tube for a heat transfer device produced of two thin metal sheets.
In commonly assigned German patent application P 195 40 683.4 and counterpart U.S. patent application Ser. No. 08/743,002, the disclosures of which are expressly incorporated by reference herein, lugs are mounted in pairs on thin metal sheets and diverge in a V-shape in the flow direction. These lugs extend to approximately a quarter or a third of the height of the rectangular tube so that they have a height which is clearly higher than the sheet thickness. In the above-referenced patent application, these lugs are provided particularly as inserts which are mounted on the thin metal sheets when the rectangular tubes are joined or before.
It is an object of the invention to provide a process of the initially mentioned type which can be implemented in an economical manner.
This and other objects have been achieved in that the lugs and/or projections are formed out of the metal sheet by means of massive forming, for example extrusion.
The process according to the invention has the advantage that the lugs and/or projections cannot only be mounted on a thin metal sheet or thin sheet metal strip in a simple manner and at reasonable cost but that also the lugs and/or projections are massive parts which internally adjoin the thin metal sheet without gaps or the like. As a result, no points are formed which are subject to corrosion.
As a further development of the invention, in the area of the lugs and/or projections, the thin metal sheet is loaded by means of a top die or a bottom die in a plane manner beyond its yield point, in which case a portion of the sheet metal material is pressed into one or several recesses of the bottom die and/or top die which, as negative molds, correspond to the lugs and/or projections to be mounted. As a result, lugs and/or projections can easily be mounted on the thin metal sheet while maintaining relatively narrow tolerances.
An advantageous application of the thin metal sheets and particularly of the thin sheet metal strips produced according to the process of the invention is the fact that a rectangular tube for a heat transfer device, particularly for an exhaust gas heat transfer device, is assembled of two U-shaped thin sheet metal shells, in which case lugs arranged in pairs project at least from the bottom of one of the thin sheet metal shells toward the inside, diverge in a V-shape in the flow direction and by means of massive forming are molded out of the bottom of at least one of the thin sheet metal shells.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.